Field of the Invention
The present disclosure relates to an inverter apparatus, and particularly to an inverter apparatus for driving a three-phase alternating-current (AC) motor.
Description of the Background Art
Conventionally, an electric motor is driven using a PWM (pulse width modulation) control inverter apparatus including a power transistor and an IGBT (Insulated Gate Bipolar Transistor) each for a switching element. In the case where the electric motor is driven using such an inverter apparatus, a surge voltage is generated, so that a motor coil may be damaged or an electric breakdown may occur.
For example, Japanese Patent Laying-Open No. 06-38543 discloses a surge voltage suppression apparatus having a reactor provided on the inverter output side and operating an electric motor by applying an inverter output voltage to the electric motor via a cable having such a length as to form a line reactor in the reactor.
In some inverters, smoothing capacitors may be connected in parallel between an inverter circuit formed by a combination of a plurality of semiconductor elements (switching elements) and a power supply (battery). It is known in this case that the capacitor includes a resistance component referred to as an “equivalent series resistance (ESR)” and resulting from the resistance of an electrode, the characteristics of a dielectric, and the like, wherein this ESR can be negligible at room temperature to elevated temperature, but may be increased to a non-negligible value as the temperature lowers (for example, 0° C. or lower).
Also, when the electric motor is driven using the above-described inverter apparatus, a motor current flows into and out of the capacitor, thereby generating a surge voltage resulting from the ESR. When the surge voltage exceeds a breakdown voltage of the semiconductor element and the like, the semiconductor element may be damaged. Accordingly, in the case where a motor current is supplied to the electric motor by controlling the inverter apparatus including a capacitor at the input side of the inverter circuit when the environmental temperature is relatively low, the influence caused by the ESR of the capacitor should be taken into consideration.
Accordingly, in order to prevent the components of the inverter apparatus from being damaged by a surge voltage generated by the ESR of the capacitor at the time when the environmental temperature is relatively low, conventionally, the maximum value (limitation motor current value) of the motor current that can be supplied to the electric motor at each temperature is produced as a map, and the inverter apparatus is controlled based on this map. Specifically, a warm-up operation of the electric motor is performed while limiting the motor current to thereby raise the temperature of the capacitor, and after that, a normal operation is performed.
However, in the case where the electric motor is used in a more severe low-temperature environment, the motor current that can be supplied to the electric motor is further decreased, thereby lengthening the time period of the warm-up operation of the electric motor. This results in a problem that it takes more time to start-up the electric motor.